长期施氮对太岳山油松林凋落物量的影响

Effects of long-term nitrogen addition on litter production of Pinus tabuliformis forests in the Taiyue Mountain

为揭示长期施氮对油松林凋落物量的影响,在山西省太岳山油松天然林和人工林中进行了长达7年的氮添加控制试验,包括对照(CK)、低氮(LN)、中氮(MN)和高氮(HN)4个水平,分别为0、50、100、150 kg N·hm^(-2)·a^(-1)。于2015—2016年对不同处理的凋落物产量组分的月动态进行监测。凋落物产量组分主要分为叶、枝、果、花、皮、杂物(动物残体、芽鳞、碎屑等统称)。结果表明,施氮显著提高了天然林年均凋落物量:HN(3.69 t·hm^(-2)·a^(-1))>MN(3.12 t·hm^(-2)·a^(-1))>LN(3.02 t·hm^(-2)·a^(-1))>CK(2.68 t·hm^(-2)·a^(-1));而人工林年均凋落物量随N添加水平呈现出先升后降的趋势:LN(3.11 t·hm^(-2)·a^(-1))>CK(3.08t·hm^(-2)·a^(-1))>MN(2.92 t·hm^(-2)·a^(-1))>HN(2.60 t·hm^(-2)·a^(-1))。这表明过量的氮输入会降低人工林凋落物的产量。年均叶凋落量所占比重最大,达总凋落量的68.3%～75.4%,果凋落量占总凋落量的6.7%～17.8%。方差分析表明,氮添加处理对叶、果和皮凋落量具有显著影响。凋落物月动态表现为双峰型,高峰期在6月份和10月份。总之,在天然林中,凋落物产量随着施氮浓度的增加显著升高(P<0.001);在人工林中,施氮处理未对凋落物产量产生显著影响(P>0.05)。

To reveal the effects of long-term nitrogen (N)addition on litter production of Pinus tabuliformis forest,a 7-year N addition experiment was carried out in natural and planted forests in Taiyue Mountain,Shanxi Province,which included four levels of N addition (CK,0;LN, 50;MN,100;HN,150kg N ·hm^-2·a^-1).Litter components were divided into leaves,bran- ches,fruits,flowers,barks,and miscellaneous (animal debris,bud scales,and other debris). Litter biomass was monitored monthly from 2015tO 2016.The results showed that N addition sig- nificantly increased mean annual litterfall biomass in the natural forest,with the order:HN (3.69 t·hm^-2·a^-1)>MN (3.12t·hm^-2·a^-1)>LN (3.02t·hm^-2·a^-1)>CK (2.68t·hm^-2·a^-1).In the plantation,the mean annual litter production increased but then decreased with the increasing N gradient,with the order:LN (3.11t·hm^-2·a^-1)>CK (3.08t·hm^-2·a^-1)> MN (2.92t·hm^-2·a^-1)>HN (2.60t·hm^-2·a^-1),indicating that excess N application can reduce the litter biomass in the plantation.The proportion of mean annual leaf biomass was among 68.3%-75.4%,and fruit biomass ranged from 6.7%to 17.8%.Nitrogen addition significantly affected litter biomass of leaf,fruit and bark.The temporal variation of total litter biomass was a double-peak pattern with peaks in June and October.In conclusion,litter production was signifi- cantly increased with increasing N level in the natural forest (P<0.001),but no significant effect was found in the plantation (P>0.05).